The Collaborative International Dictionary of English v.0.48:

Nehushtan \Ne*hush"tan\, n. [Heb.]
   A thing of brass; -- the name under which the Israelites
   worshiped the brazen serpent made by Moses. --2 Kings xviii.
   4.
   [1913 Webster] Neif

Easton's 1897 Bible Dictionary:

Nehushtan
   of copper; a brazen thing a name of contempt given to the
   serpent Moses had made in the wilderness (Num. 21:8), and which
   Hezekiah destroyed because the children of Israel began to
   regard it as an idol and "burn incense to it." The lapse of
   nearly one thousand years had invested the "brazen serpent" with
   a mysterious sanctity; and in order to deliver the people from
   their infatuation, and impress them with the idea of its
   worthlessness, Hezekiah called it, in contempt, "Nehushtan," a
   brazen thing, a mere piece of brass (2 Kings 18:4).


Hitchcock's Bible Names Dictionary (late 1800's):

Nehushtan, a trifling thing of brass